A photodetector is typically composed of a thin semiconductor body with a semiconductor junction, for example a P-N junction, therein and with electrical contact being made to the light entry surface and the opposed, or back surface, of the body. Photodetectors typically exhibit a conversion efficiency of light energy to electrical power less than the theoretical maximum because the absorption coefficient of the body for light in a particular range of wavelengths is too small. This effect may be compensated for by using for the back electrical contact a material, such as a metal, exhibiting high reflectivity so that the transmitted light is reflected back into the body. However, most contact materials do not efficiently reflect light at this interface or may degrade the performance of the semiconductor body during subsequent processing steps in the manufacture of the photodetector. Alternatively, the light entry surface or the back surface of the photodetector, or the surface of a substrate upon which a body is deposited may be roughened using chemical etching techniques. The use of chemical etching techniques is undesirable because it introduces additional steps in the manufacture of the photodetector and the etching technique itself may degrade the performance of the photodetector.
It would thus be desirable to have a photodetector in which the absorption in the semiconductor body is increased over the range of wavelengths in which light is weakly absorbed, while at the same time minimizing the number of steps needed to manufacture the device and reduce the undesirable side effects, such as degradation of performance, which the additional processing may cause.